CNN's ratings woes continue to get worse. Following last week's news of a 15-year primetime low during Piers Morgan, final Nielsen ratings give the network its lowest-rated weekday primetime showing among total viewers in more than 20 years.

The network averaged just 395,000 viewers in P2+ during the 8-11 p.m. block between May 14 and May 18, dipping below the previous low (over the 2010 Christmas holiday) by nearly 20,000 viewers. Programming in that block, Anderson Cooper’s AC360 and Piers Morgan Tonight, didn't fare much better among the targeted adults 25-54. With just 111,000 viewers in the group, it also ranks as the fourth-lowest week in the key demo.

Looking at the whole week, it marked the lowest seven-day haul for the network since March 1997.

Having already posted its lowest-performing month in a decade in April, four of CNN's 10 weakest weeks of the past 20 years have fallen in 2012. In the demo, it isn't faring quite as bad, with just two weeks of the year in its bottom 10.